The present invention relates to an orthopaedic clamped connection as a functional element for force transmission in a prosthesis, of the general type comprising a tube socket and a tube made of light metal.
Such a clamped connection is described in EP-A2 0 694 295. This document discloses an axially slit tube socket which can be circumferentially tensioned by means of a clamping screw. The socket is adjoined at one end by an annular coupling section which on its circumference has four threaded holes, each to accommodate a coupling and adjustment screw, and on the end face has an annular ball socket to rest against a ball joint of an adjustment body which, in the coupling position, has a projection configured as a multiface pyramid projecting into the clamping region of the clamping screw. The free end section of the tube socket opposite the coupling section is provided on its inner annular surface with a plastic clamping sleeve which can be configured as a separate ring or as an inner coating. The axial length of the plastic clamping sleeve corresponds approximately to one fifth of the axial length of the tube socket. As a result of this design, clamping no longer occurs directly at the end of the tube but at a distance therefrom, so that the tube section lying between the plastic clamping sleeve and the coupling section can be subjected to elastic deformation. In the region of the highest relative movement between the tube socket and tube end, metallic contact between these two parts is prevented by the plastic clamping sleeve. Dynamic flexural tests have shown that this considerably increases the life of said components.
This previously known solution has been found to be useful in principle, but other disadvantages have to be accepted in order to attain the advantages mentioned. Thus, the sleeve as a separate plastic ring requires a lengthening of the adapter and thus higher manufacturing costs and a higher weight. The plastic sleeve itself can have stresses and can be out-of-round as a result of the manufacturing process, which can lead to problems in assembly. When the sleeve is configured as a plastic layer, the achievable tolerances are unsatisfactory; an excess therefore has to be applied and subsequently machined away. Moreover, a plastic sleeve can suppress frictional corrosion to only a limited extent.